In today's computer systems, some computer system component interconnect protocols provide techniques to establish and to maintain synchronization. One such protocol is the Serial ATA protocol (Serial ATA Specification rev. 1.0 released Jun. 28, 2001). This protocol allows communication between two devices such as a disk controller and a disk drive. The Serial ATA specification provides for a serial interconnect using differential pair signaling. The Serial ATA specification further provides for periodic transmission of alignment primitives. The alignment primitive is a predetermined pattern of bits of a predetermined length that is recognized by devices coupled to the interconnect. The alignment primitive allows devices that have lost synchronization to recover bit-boundary alignment.
The alignment method provided for in the Serial ATA specification involves the transfer of ALIGN primitives across the interface. The ALIGN primitive is a four byte sequence. The first byte of the primitive is an encoded K28.5 character (rd+: 110000 0101; rd−: 001111 1010). The receiving device compares the first character of the incoming ALIGN primitive with the expected K28.5 character. If there is a match, then the receiving device is assumed to be synchronized.
The above mentioned method is susceptible to false detection of ALIGN primitives that are being sent at a different rate than expected, or false interpretation of noise on the interconnect wires as a valid ALIGN primitive.